Acid/base strength
You are given two acids:
Acid A has a Ka = 1.3 × 10⁻⁵
Acid B has a Ka = 6.2 × 10⁻⁴
Which is the stronger acid
Acid B
What is the definition of the equivalence point?
Moles of H+ = moles of OH-
2O(g) ⇋ O2(g) is spontaneous in the forward direction. What can we deduce about the sign of ΔSsurroundings?
ΔSsurr>0.
The second law of Thermodynamics states that ΔSuniverse=ΔSsurroundings+ ΔSsystem and that ΔSuniverse must always be increasing.
ΔSsys becomes negative (fewer gas molecules), so ΔSsurr must become positive to allow ΔSuniv to increase.
Calculate the Gibbs free energy change (G) for the following chemical reaction:
glutamate + NH3 —--> glutamine + H2O
The reaction occurs at 37°C, the change in heat (H) = 2.8 kJ/mol, and the change in entropy (S) = 5.6 J/K*mol.
1.1 kJ/mol = 1100 J/mol
Which of the following statements is false:
(i) The rate of a reaction depends on the energy of collisions between reactants.
(ii) The rate of a reaction depends on the orientation of colliding molecules.
(iii) The rate of a reaction depends on the energy difference between the reactants and products
FALSE: (iii) The rate of a reaction depends on the energy difference between the reactants and products
it depends on the activation energy: the energy difference between reactants and transition state(s)
Which factors determine the strength of a binary acid (H-X), and which factors help determine the strength of oxyacids (H-O-X)? Explain the relationship.
A. Electronegativity of X
B. Bond strength between H and X
C. Atomic radius of X
Binary acids: B and C
larger radius --> weaker bond --> increasing acid strength
Oxyacids: A
More EN X pulls electron density away from O-H bond --> easier to lose proton --> stronger acid
Consider the titration of 50.0 mL of 0.120 M HNO2 with 0.200 M KOH.
Draw the titration curve for this titration.
Should look like the titration curve of a weak acid and strong base:
- noticeable buffer region before equivalence
- higher initial pH
- pH of equivalence point >7
A reaction is nonspontaneous at low T but becomes spontaneous at high T.
What must be true about the signs of ΔH and ΔS?
ΔH > 0 and ΔS > 0
If the reaction “turns on” at high T, the TΔS term must eventually overpower ΔH.
At what temperature (in oC) does a reaction go from being nonspontaneous to spontaneous if it has
ΔH = 284 kJ/mol and ΔS = 986 J/(K*mol)
15oC
Which of the following solutions will have the lowest freezing point?
(A) 0.010 m RbI
(B) 0.015 m SrBr2
(C) 0.035 m CH3OH
(B) 0.015 m SrBr2
Given the following list of acids, which one would produce the conjugate base that forms the most basic aqueous solution at equal concentrations?
H2O, NH4+, HCN
H2O
The weakest acid yields the strongest conjugate base
A 25.0 mL of a 0.10 M HCl solution is titrated with a 0.10 M NaOH solution. Calculate the pH after 5.00mL of NaOH solution have been added.
pH = 1.17
One statement contradicts the other 3. Which is it?
ΔGo < 0
lnK > 0
ΔSo > ΔHo/T
K < 1
K < 1
All other answer choices are consistent with a reaction that is spontaneous in the forward direction. A spontaneous reaction under standard conditions (ΔG° < 0) must have K > 1
VERBALLY explain how you would solve this problem:
This reaction occurs at 298K. Find ΔGo and determine if it is thermodynamically favorable.
CH4(g) + 2O2(g) ⇋ CO2(g) + 2H2O(g)
ΔHof: -75 kJ 0 kJ 393.5 kJ -242 kJ
ΔSof: 186 J/K 208 J/K 214 J/K 184 J/K
1) Use these equations and plug in the given enthalpy and entropy of formation values:
ΔH∘ = ∑(n⋅ΔHf∘(products)) − ∑(m⋅ΔHf∘(reactants))
ΔS∘ = ∑(n⋅ΔSf∘(products)) − ∑(m⋅ΔSf∘(reactants))
2) Then plug what you know into ΔGo=ΔHo−TΔSo
3) If ΔG is negative, then it is thermodynamically favorable
Draw the Lewis structure of HCN and its conjugate.
see slides for answers